Optical fiber connectors are used in a variety of telecommunications applications to connect one optical fiber to another, or to connect an optical fiber to a telecommunications device. Certain optical fiber connectors such as mechanical splice connectors include a short section of single-mode optical fiber (SMF) called a stub fiber that interfaces with a field optical fiber that is inserted into the connector in the field by the end-user. When a connector is operably connected (mated) to another connector, the stub fiber resides between the field fiber of its own connector and the stub fiber of the mating connector.
When all the optical fibers are aligned and otherwise matched in size and configuration, the light travels in the field and stub fibers in the lowest or fundamental mode, namely the LP01 mode. However, a misalignment, a mismatch in the mode-field diameter (MFD) of the fibers, or a combination of these and other factors, can cause light to travel in higher-order modes, such as the LP11 mode for a short distance even though the fibers are SMFs. Thus, though an optical fiber may be designed to be an SMF, there are circumstances under which they operate as multimode optical fibers.
Coherent light traveling in different guided modes takes different optical paths and can cause multi-path interference (MPI). MPI can cause light transmitted through the connector to have significant time-dependent fluctuations that are exacerbated by the use of off-the-shelf SMFs designed for long-haul telecommunications applications. MPI and the attendant power fluctuations are undesirable and degrade the performance of the telecommunications system in which the optical fiber connector is used.